Fabrication of quartz resonators



Patented May 15, I

UNITED STATES zsiaz a ra'nmcarron or omiarz RESONATORS Arthur F. Winslow, Scotia, N. Y., assignor to General Electric Company, a corporation of New York I No Drawing.

3 Claims.

The present invention relates to the fabrication of quartz crystals for electric oscillators.

In accordance with one method of fabricating quartz crystal dielectric elements for electric unit of time was not uniform and an undesirable in characteristics results when a batch of oscillator elements of the same size is subjected simultaneously to the same hydrofluoric acid treatment for the same length of time. In other words, the time required to produce a desired increase in vibration frequency cannot accurately be predetermined under such conditions.

In accordance with my invention the chemical activity between silica articles being treated and the acid etching reagent is regulated by associating the acid reagent with an effective amount of.

ammonium biiluoride which. functions as a stabilizer. 1

As a consequence. of my invention the etching efl'ect, or removal of silica from the surface at an article of crystalline silica, is rendered uniform indistribution and occurs with a uniform. ratewhich makes it possible to secure a prede termined result. in.-a.given time. v

In'carrying out my invention resonator elements of quartz are fabricated by cutting and rough grinding the'oscillators to approximately a desired order of frequency. for example, to approximately 6000 kilocycles. As'is well known. the frequency of piezo-electric oscillation is critically dependent on the thickness of the oscillating dielectric elements. If a slightly higher frequency is desired, careful grinding by highly skilled operators is required until the desired frequency is attained. Chemical reduction in if accurately controllable, permits Application January 28, 1944, Serial No. 520,139

further approximation of desired frequency by unskilled labor with greater speed and dependability. However, the flnal accurate adjustment of dimensions of the resonator to obtain exactly a desired frequency may be carried out by a hand-lapping operation.

7 If considerable abrasive from a grinding operation is embedded in the surface of the quartz blanks as a result of the rough grinding, then, preliminary to subjecting the blanks to a timed acid treatment, the abrasive should be removed by a cleaning operation in an etching reagent. It is also desirable. that oil or grease on the surface, even in the minute amounts derived from the skin when handling blanks, should .be removed-before subjecting the blanks to the etching reagent. This may be done by washing with acetone.

. The clean crystals are subjected for a predetermined period of time at room temperature to the etching bath comprising an aqueous solution of hydrofluoric acid and ammonium acid fluoride (NHiHFz). Concentrated hydrofluoric acid is preferred as with weak acid the process is too slow. Commercial hydrofluoric acid consisting of an aqueous solution of HF containing about 47 to53 per cent of hydrofluoric acid may be used. It should be saturated with ammonium bifluoride. About '35 grams of the ammonium bifluoride is dissolved in a suflicient amount of 31c commercial acid to produce 100 cc. of solu- The etching rate of a given reagent may be determined by measuring the frequency of a chosen 35 oscillator plate, exposing it for a. given length of time, for example one minute, to the etching effect of the reagent, and then, after carefully cleaning the plate; again determining the freis reproducible with time, as is true when using the mixture abovegiven, then a multiple of the unit time will give a predictable incr e of frequency. with a quartz .oscillator crystal oscfl lating at 2500 kc., the etching rate at 25 C. may

=5 be produced either by moving the quency of oscillation. When the etching ratebe Like. per minute while an oscillator 0t 4600 kc. may have an etching rate of 1.8 kc.

ing to renew the solution in contact with the surfaces to be dissolved cnclto Torush away gas huhlales. The duration of the treating time will very in accordance with the conditions, such for exnmple as the temperature of the reagent, the amount of material to be removed and the concentration oi the reagent, but in general it may he said that the duration of etching ordinarily will fall within the limits of about ten minutes to one hour. For example, if a frequency of 6030 kc. is desired, a. plate which resonates at 6000 kc.

- may be exposed to the etching reagent for about ten minutes.

As the construction of piezo-electric oscillators containing dielectric elements consisting of thin plates of crystalline quartz ore well'understood in the art, it is not necessary to described them in connection with the present method.

With a predetermined set of conditions for the etching, it is possible by the practice of my invention to predetermine the amount oi materiel removed during a given period and thereby to upproxlmateclosely the frequency desired in the oscillating elements. The amount of skilled hand labor for the dual adjustment oi frequency thus is reduced to u minimum;

Quartz oscillator plates or other shaped quartz articles after being treated by contact with o. reagent embodying my invention have u smoot Polished surface.

The concentration of the solution as etching "proceeds should be restored by approximatemeasures as the .reaction proceeds in quantity production, for example'by introducing anhydrous hydrofluoric acid to replace acid lost by reaction with the silica.

After the etching has been completed, the oscillator element should he very carefully cleaned to remove traces of reagent. It is desirable to rinse first with distilled water, then with a dilute solution of ammonium hydroxide, then to again wash. with water, which preferably should be lilanlrs or icy stirring the solution, the object ice-=- heated, and finally to rinse with acetone. rinsing operation, after the etcc has com pleted, may. he carried out in some case icy h ing the completed elements for about ten mhcu Us in a relatively large quantity of distilled Water.

Careful and thorough cleaning: is desirohle to maintain the acidity or livelinesc of oscillction of the quartz resonators.

What I claim as new and desire to secure by Letters Patent of the United Stotec is:

l. The method of fabricating resonates crystalline quartz which consists in mcchu shaping said articles to approximate jecting the shaped articles to the diccolvlno tion of an aqueous solution of hydrofluoric and ammonium bifiuoride until u c has been further approximated, sold resonators with sumcient thoroughness to re movev traces of adhering reagent and flnrdiy com plcting mechanically accurate dimensional sizing oi sold resonators.

2. The method oi effecting desired change piezo-electrivibration frequency of" crystalline quartz resonator elements which consist-sin immersing said elements in an aqueous solution Suhstairtiully saturated with hydrofluoric-acid and ammonium bii'luoride and having a. substantially constant predetermined chemical activity and removing said elements upon the elapse of o. cal-- culated time interval whereby at desired dimer1- V clonal reduction is attained. 

